This invention relates to a method and apparatus for zig-zag folding and, more particularly, constitutes an improvement over my prior U.S. Pat. No. 3,195,882. In that patent, to achieve higher speeds, the tip of the gripper anvil traced an envelope having a greater diameter than the envelope traced by the tucker tip. This represented a departure from the prior art which itself was improved by my prior U.S. Pat. No. 3,489,406. However, both of these patents deal with mechanically controlled grippers as contrasted to the resilient form of gripper of my U.S. Pat. No. 3,947,013.
The instant invention has to do with the first type of folding wherein the grippers are mechanically controlled. However, notwithstanding the precision ostensibly available from mechanically controlled grippers, it has become increasingly difficult to develop folds at precise locations, i.e., along spaced apart lines of transverse perforation.
It will be appreciated that a great demand exists for zig-zig folded forms for use in computers. Computers, particularly the print-out mechanisms, have been operating at ever-increasing speeds. Anything that interferes with the achievement of the higher speeds is, of course, undesirable and disadvantageous. One of these undesirable phenomenon is that of stack "lean". By this, I refer to the fact that a free-standing stack, when viewed from the side, and parallel to the fold lines, assumes a parallelogram type of contour rather than the desired rectangle. This can be noted quickly during the process of manufacture but heretofore nothing has been done to correct this without stopping the machine.
I have ascertained that stack "lean" results from alternate forms or folds being longer than those intervening. The length of forms or folds normally is determined by the lines of transverse perforation existing in the sheet, and I have noted that in prior folders, the tucker and gripper about to enter into engagement "hunt" to find the line of perforation, i.e., the weakest area in the portion of the web being folded. The difference in length between adjacent lines of perforation in adjacent forms may be only of the order of a few thousandths of an inch but it still results in the undesirable stack "lean".
I have ascertained that the undesirable "lean" which can disrupt the operation of the computer print mechanism by virtue of failing to feed properly, can be overcome by a slight annular shift of one folding member relative to the other provided certain geometrical relations are present--and this during operation so that the results thereof can be immediately ascertained.
Here it will be appreciated that there has been a demand for increasing speeds of production because there has been a shift to single part business forms--the ease and economy with which reproduction can be made by xerographic type machines making it unnecessary to have multiple part forms. Thus, to maintain a given output of business forms, the forms manufacturer is desirous of operating at higher speeds which is reflected in differential tensions in the web which can result in slight mislocations in the lines of transverse perforation. Even where the lines of perforation are exactly spaced, lean may result from the operation of the folder. So the invention is concerned with correcting lean irrespective of the cause.
For example, I have noted machines that were able to produce straight stacks up to 800 FPM but leaning stacks occurred at 1000 FPM. Two-wide folders may have one folder that produces straight stacks under certain conditions while the other produces leaning stacks. Change of parent rolls often changes the end product from straight to leaning stacks. All in all it can be and often is a costly, time consuming, as well as an exasperating thing to try to analyze and correct.
With my system there is no need to analyze the reason why a folded stack is leaning. The operator simply turns a handwheel a bit while the machine is operating at full speed and the correction is made.
The problem of stack "lean" is substantially eliminated in the system described through the use of helical mating gears on the folding members whereby very slight angular adjustments can be made "on the fly". Such type of gearing has not been used, to the best of my knowledge, on folding rolls although such gearing has been used in adjusting the mating engagement of perforation rolls.
Throughout the years, this has not been achievable and I have discovered that this stems from the fact that all the prior folders provided surplus web material above the folding rolls. For example, one widely employed folder is seen in U.S. Pat. No. 2,626,145 and the operation there involved the web-delivering means being actuated so as to deliver the web at a rate of travel greater than the rate of travel of the gripper jaws.
The system of this invention which makes possible the angular adjustment to correct lean requires that the outer edge or the tip of the gripper anvil travel at web speed, the tolerance being plus nothing to a few thousands of an inch minus per foot of web.
Further, as the tucker edge forces the perforated line of the web down between the gripper anvil and the gripper to its deepest penetration the distance between the outer edge of the gripper anvil and the tucker edge must remain constant. In the meantime the gripper which is cam actuated but spring loaded against the tucker is keeping a constant distance between the tucker and gripper edges.
Thus, from the instant that the tucker blade edge contacts the paper to the point of deepest penetration there is no relative movement or slippage between the web and the tucker edge. As the web will fold at the part of perforation that contacts the tucker edge it becomes possible by a slight angular movement of the tucker relative to the gripper to create a different fold line within the limits of the perforation width. Also, it is to be realized that the perforated line does have width. This width increases as the edge of the perforating blade wears to a distinctive flat after a few hours of use.